1. Field of the Invention
The present invention relates to a method for inspecting a polishing pad, an apparatus for performing the method of inspecting, and a polishing device adopting the apparatus, which can prevent wafer defects during wafer polishing operations.
2. Description of the Related Art
During a conventional semiconductor manufacturing procedure, processes such as lithography, light exposure, ion implantation, chemical and mechanical polishing, chemical or physical deposition, and plasma etching, are performed on wafers to form semiconductor chips and devices. In particular, chemical and mechanical polishing processes are widely used for manufacturing the semiconductor device, because the chemical and mechanical polishing process can be carried out at a low temperature and a large area of the wafer can be planarized.
FIG. 1 shows a conventional polishing device for manufacturing a semiconductor device. In FIG. 1, a platen 12 is provided with a polishing pad 10 which makes contact with a wafer W. A motor 14 rotates the platen 12, so that the polishing pad 10 attached on the platen 12 polishes the wafer W. A polishing head 16 fixes the wafer W via suction during the polishing process. The polishing head 16 rotates while urging the wafer W toward the platen 12. A polishing pad conditioner 18 is installed along a side of the polishing pad 10 for periodically conditioning the polishing pad 10. The polishing pad conditioner 18 is pressed toward the polishing pad 10, and is conditioned by means of a diamond disc formed within the surface of the polishing pad conditioner 18. A slurry supply 20 provides slurry to the polishing pad 10 during the polishing operation.
In operation, polishing head 16 fixes the wafer W in place via suction, then the polishing head 16 and the polishing pad 10 are rotated so as to allow the wafer W to contact the polishing pad 10. At the same time, the slurries are supplied onto the polishing pad 10 and the slurries are distributed radially outward along the polishing pad 10 surface as a result of the rotation of the polishing pad 10, thereby promoting the polishing of the wafer W. The polishing pad conditioner 18 is brought into contact with the polishing pad 10 at periodic intervals so as to prevent the polishing pad from wearing unevenly.
While the polishing process can planarize a large area of the wafer W, there is a drawback. Since the polishing pad 10 directly contacts the wafer W, the wafer W may be scratched if the surface of the polishing pad 10 has a defect, or particles introduced from the exterior are attached on the surface of the polishing pad 10. Such defects can lower the production yield of the semiconductor device.
Typically, in order to check for defects on the polishing pad 10, an operator examines the polishing pad 10 with the naked eye, or the operator inspects the surface of the wafer W after the polishing process has been finished. However, checking the polishing pad 10 with the naked eye takes a lot of time, and it is difficult to attain an accurate measurement because of the vagaries inherent in a process requiring human intervention.
Various kinds of solutions have been disclosed in an effort to prevent the wafer from being scratched during the polishing process. For example, in U.S. Pat. No. 5,708,506 issued to Birang, the roughness of the surface of the polishing pad is measured using an optical device so as to control the conditioning process to prevent wear on the polishing pad. U.S. Pat. No. 6,045,434 issued to Fisher, Jr. et.al., discloses an apparatus for conditioning the polishing pad by measuring the variation of the thickness of the polishing pad during the polishing process. Also, Korean Patent Laid-Open Publication No. 1999-25212 discloses a method for determining the replacement period of the polishing pad by measuring the profile of the polishing pad.
However, though the above apparatuses can improve the surface uniformity and control the thickness of the wafer, scratches may still be generated on the surface of the wafer.
In view of the shortcomings and drawbacks of the prior art, it is an object of the present invention to provide a method for inspecting a polishing pad so as to reduce wafer defects during a polishing process.
Another object of the present invention is to provide an apparatus for inspecting the polishing pad so as to reduce wafer defects during the polishing process.
Still another object of the present invention is to provide a polishing device which polishes the wafer while inspecting the polishing pad.
To accomplish the first object of the present invention, there is provided a method for inspecting a polishing pad. According to the method, reference data are obtained from a surface of a normal polishing pad, which does not generate wafer defects during the polishing process. Empirical data are then obtained from a surface of a polishing pad to be inspected. Then, the state of the polishing pad is determined by comparing the reference data of the normal polishing pad with the empirical data of the polishing pad to be inspected.
To accomplish the second object of the present invention, there is provided an apparatus for inspecting a polishing pad including an optical data gathering part for obtaining optical data from two sources: (1) reference data from a surface of a normal polishing pad, which does not generate wafer defects during the polishing process, and (2) empirical data from a surface of a polishing pad to be inspected. A defect profile, or defect state, is attained by comparing the reference data with the empirical data of the polishing pad outputted from the optical data gathering part.
To accomplish the third object of the present invention, there is provided a polishing device including a polishing head which fixes a wafer thereto via suction, and rotates the wafer while pressing the wafer against a polishing pad positioned in a platen. The platen is also rotated by a rotating shaft attached thereto. An optical data gathering part obtains optical data from two sources: (1) reference data from a surface of a normal polishing pad, which does not generate wafer defects during the polishing process, and (2) empirical data from a surface of a polishing pad to be inspected. A defect profile, or defect state, is attained by comparing the reference data with the empirical data of the polishing pad outputted from the optical data gathering part.
The polishing pad is preferably inspected for defects before the polishing pad is placed on the polishing device so as not to cause wafer defects while the inspection is being conducted. The operator can also choose to inspect the polishing pad for defects during any idle time of the polishing process, or after the polishing process. In this way, the operator can quickly take follow-up measures when a defect is found in the polishing pad. Accordingly, the wafer is prevented from being scratched during the polishing process.